I second this. I love the black and white.
The only immediate tweak I would right now is to have the checkpoints be a different color (the black poles look like obstacles at the moment).
I understand that you may be tempted to add realistic textures, but imho you are passing on a golden opportunity to really stand out visually by not being just another game going for realistic textures. Keep it black and white and invest in some black and white visual effects to make the visuals standout a bit. (maybe some kind of shadowing/negative effects, and maybe some grey/white particle effects like a subtle dust puff when landing the tires on the ground. Even go a bit cartoony with some rough straight edges or something.)
Just keep in mind: you already did the hardest thing: translate the trial experience into "realistic" but learnable and intuitive controls. that is no mean feat. The bike/rider balance is also spot on. I do believe that if you put a solid scoring/evaluation/challenge system on top of this you have the potential to become to the Trials Series what Skate is was to the Tony Hawk Series.
It's incredible to me that after 1 minute of learning the bunny hop move (on keyboard of all things) I had already created a flow of key presses that made the bunny hop just seam effortless. Although you are using way too many keys compared to what I would normally tolerate in a game, here you have just nailed the execution so well.
This game really deserves a polished release. I insist, don't focus on adding realistic graphics, players often don't know what they want until you show it to them.